Silicon carbide (SiC) has the superior properties of having insulation breakdown voltage roughly ten times stronger and bandgap roughly three times larger than silicon (Si), and is expected to be used in applications such as power devices, high-temperature operation devices.
These SiC devices are normally fabricated using SiC epitaxial wafers obtained by growing a SiC epitaxial film serving as the active region of the device by a method such as chemical vapor deposition (CVD) on a SiC single crystal substrate obtained by processing SiC bulk single crystals grown by a method such as sublimation recrystallization.
SiC single crystal substrates contain numerous crystal defects, and these crystal defects are known to propagate to the epitaxial film. Consequently, technologies have been developed for improving the quality of epitaxial films in consideration of this propagation.
Known examples of methods used to non-destructively detect crystal defects such as dislocations or stacking faults contained in SiC single crystal substrates and SiC epitaxial wafers, where an epitaxial film is formed on the substrate, include X-ray topography (Non-Patent Documents 1 and 2) and photoluminescence (Patent Document 1).
Three types of dislocations (consisting of threading screw dislocations (TSD), threading edge dislocations (TED) and basal plane dislocations (BPD)) are known to be present as linear crystal defects in SiC single crystals. TSD are dislocations in which the Burgers vector that propagates in the direction of the c-axis is <0001> or double thereof. TED are dislocations in which the Burgers vector that propagates in the direction of the c-axis is ⅓<11-20>. BPD are Dislocations in which the Burgers vector present on the c-plane is ⅓<11-20>.
SiC epitaxial films are typically formed by using a surface in which step density has been intentionally increased by inclining a SiC single crystal substrate from the (0001) plane (c-plane) in the direction of <11-20> at an off angle of within 10° as a growth surface, and growing crystals in the horizontal direction of the step (step flow growth).
Since a surface having an off angle with respect to the c-plane is used for the growth surface in this manner, basal plane dislocations (BPD) present on the c-plane are exposed on the growth surface. In addition, threading screw dislocations (TSD) and threading edge dislocations (TED) extending in the direction of the c-axis are also exposed on the growth surface.
Basal plane dislocations (BPD) that have propagated to an epitaxial film are not stable in the epitaxial film and easily degrade to two energetically advantageous Shockley partial dislocations, resulting in the formation of stacking faults between these two Shockley partial dislocations. Since stacking faults act as carrier lifetime killers, current ends up concentrating in those regions where stacking faults are not present, and as a result of a decrease in the surface area where current flows, on-resistance ends up increasing. Moreover, in bipolar devices such as pn diodes, one of the aforementioned two partial dislocations has Si as the core thereof while the other has C as the core thereof. Therefore, only the partial dislocation having a Si core migrates due to recombination energy of electrons and holes, and the area of the stacking fault ends up increasing (Non-Patent Document 3).
In addition, carrot defects present in epitaxial films are known to be formed by interaction between basal plane dislocations (BPD) and threading screw dislocations (TSD) of SiC single crystal substrates.